CS452 datasheet(4/5 Pages) CHERRY

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The CS452/453 is provided with an input lead (VIN) which

turns the injector driver ÓonÒ and ÓoffÒ. This lead has a

nominal trip level of 1.4V and an input impedance of

20k½. It is internally protected against negative voltages

and is compatible with TTL and most other logic.

There is also a control lead (CONTROL) which if held low

or grounded, permits the device to operate in saturation to

Ipk(sense), where it will switch to Isus automatically. If CON-

TROL is brought high (>1.5V), the output drive stage is

turned off, regardless of what state the input (VIN) is at,

and the output current goes to zero.

Figure 1 shows the operating waveforms for the simplest

mode; i.e., with CONTROL grounded. When the driver is

turned on, the current ramps up to the peak current sense

level, where some overshoot occurs because of internal

delay. The CS452/453 then reduces its output to Isus. The

fall time of the device is very rapid (²1.0µs), but the decay

of the load current takes 150 to 220 µs, while dumping the

load energy into the protection Zener clamp.

It is essential that the Zener voltage be lower than the

V(BR)CEO(sus), but not so low as to greatly stretch the load

current decay time. Without the zener, the discharge of the

load energy would be totally into the CS452/453, which, for

the high current applications, could cause the device to fail.

Also in figure 1 is the graphically derived instantaneous

power dissipation of the CS452/453. It shows that, for

practical purposes, the worst case dissipation is less than

(Isus) (VBAT) (duty cycle).

Figure 2. Switching Waveforms (Expanded Time Scale)

Figure3. Switching Speed vs. Temperature

1.5

140

120

100

-20

-40

2.0

1.0

0.5

Case Temperature (ûC)

90%

1.0

2.0

3.0

Ipk

10%

Vl Turn

Off

Output

Voltage

Output

Current

tv tf

Figure 4. Application of CONTROL

Provided in Figures 2,3, and 4 are definitions of the

switching intervals specified in the Electrical

Characteristics. Figure 3 shows that the critical switching

parameters stay under control at elevated temperatures.

In those applications where high voltage transients may

occur while the output lead (OUT) is in the Isus mode,

excessive instantaneous power dissipation may occur,

causing device failure. When this condition occurs, the

control lead (CONTROL) can be used to shut off the out-

put stage in order to protect the CS452/453. As long as

CONTROL is in the high state (>1.5 volts, typ.), the output

will remain off. One method of sensing the supply voltage

and controlling CONTROL is to use a resistor divider

between the supply voltage and ground with CONTROL

connected to the resistor divider (see Typical Application

diagram).

Another application option of the control lead is to use it

to accomplish an enable/disable function. Since CON-

TROL is compatible with TTL and CMOS logic levels, a

logic low will enable the output, and allow it to follow the

input signal at VIN. If CONTROL is held at a logic high,

the output will be disabled regardless of the state of the

input signal.

If the control function is not being used in the application,

it must be grounded or otherwise placed in a logic low

state. If CONTROL is left open, the output stage will

remain off.

The output current in the Isus mode should be oscillation

free. There is a possibility that in a given application, the

output current could oscillate for a small fraction of parts.

If this was to occur, the remedy is place a capacitor from

OUT to Ground. The value of the capacitor should not

exceed 0.01µF.

>1.4V

>1.5V

Ipk

Isus

Input

Signal

VIN

Control

Signal

CONTROL

Output

Current

Application Information

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